When resurfacing an asphalt road surface, at least a portion of the upper surface of the roadway is milled by specialized equipment so a new layer of asphalt can be deposited. The milling operation, which can also be referred to as cold planing, asphalt milling, or profiling, can be carried out at any desired depth depending on the resurfacing operation. Typically, a road surface is milled, and the material removed from the road is collected for recycling. Material suitable for recycling is ground and used as aggregate in new pavement. Milling operations in general are also used to control heights and clearances of other road structures such as curb reveals, manhole and catch basin heights, shoulder and guardrail heights, overhead clearances and the like in both finished and unfinished road surfaces.
Milling is generally performed by construction equipment called milling machines or cold planers. These machines typically use a large rotating drum for removing and grinding the road surface. The drum is usually enclosed in a housing that shields the surroundings from flying debris and contains the milled material, which is collected and deposited on a conveyor for loading onto a waiting truck. Many cold planers use an up-cut configuration, in which the drum rotates in the reverse direction to the drive wheel or tracks, which helps drive the milled material up and into a conveyor. This configuration also creates considerable amounts of dust and other airborne debris, which can be controlled by various methods including water spraying and using vacuum collectors. The water sprayed operates to cool the cutting drum and also help contain or settle dust. A typical cold planer will carry a water reservoir onboard that feeds the water sprays. However, cold planers may operate in remote areas where water is not readily accessible and must be delivered by truck. Water replenishment also requires the machine to stop operation and thus increase the time required to complete a project.